Partial Pupil-Sparing Vasculopathic Third Nerve Palsy: Pattern of Extraocular Muscle Involvement

In distinguishing between microvascular and aneurysmal third nerve palsies (3NP), the state of the pupil has been found to be the most helpful clinical feature. Pupil-sparing usually indicates a microvascular palsy. Occasional cases of pupil-sparing aneurysmal palsy occur when other muscles are also spared. To deal with these "exceptions to the rule," it has been suggested that all partial pupil-sparing 3NPs should be studied angiographically. The definition of "partial," however, has not been explicit: do we mean all muscles partially functioning or some muscles spared? Furthermore, would the pattern of extraocular muscle (EOM) involvement be helpful in distinguishing between microvascular and aneurysmal partial palsies?